Many types of vessels pose cleaning difficulties. One type of vessel in which particularly disadvantageous cleaning difficulties arise is a coker for use in extracting crude oil from solid materials (e.g. sand), such as a particular type of dense phase cyclone reactor coker manufactured by Exxon Corporation, for example. Such cokers typically have a plurality of “snouts” (usually 4-6 snouts) disposed circumferentially around the inside of an upper region of the coker. Each snout may include a 24 inch (61 centimetre) elbow joint for example, and is typically in communication with a respective 24 inch (61 centimetre) gas tube extending vertically downward within the coker. Below the gas tube is a void area for the cyclone effect, and a dip leg extending beneath the void area. Cokers of this type are typically on the order of 100 metres (several hundred feet) tall, and a typical distance from the top of the snout to the bottom of the dip leg may be about 85 feet (26 metres), for example.
Such cokers typically operate at internal temperatures in excess of 450° C. (approximately 850° F.), and internal air velocities in excess of 150 m/s (500 ft/s). Cokers of this type are typically designed to operate continuously, 24 hours a day, 365 days per year, with a typical output in the range of 75,000 or more barrels of crude oil per day.
Over time, however, coke deposits tend to build up within various internal components of the coker, such as the snouts, gas tubes and dip legs, gradually decreasing the efficiency of the oil-solid separation process. When the process efficiency becomes too low, the coker must be shut down for manual internal cleaning. Due to the internal operating conditions of the coker, such coke deposits are typically as hard as concrete, and are difficult to clean. Accordingly, it is not uncommon for the cleaning process for dense phase cyclone reactor cokers to take 30 days or more, resulting in tens of millions of dollars in clean-up costs and lost revenues.
One approach to this problem involves inserting a rigid pipe through a valve in a side wall of the coker, at the approximate height of the snouts (which may be about 220 feet or 67 metres above the bottom of the coker, for example). The rigid pipe is pushed into a mouth of one of the snouts, and high-pressure water is pumped through the pipe into the mouth of the snout and down the gas tube, to attempt to dislodge the coke deposits. However, although this approach is effective in removing coke from the mouth region of the snout, it is progressively less effective in removing coke from portions of the gas tube and dip leg located further down within the coker. Thus, this method merely prolongs the period of time for which the coker may be operated before a cleaning shut-down is required, rather than preventing a shut-down.
Accordingly, there is a need for an improved method of cleaning a vessel. There is also a need for a method and apparatus for cleaning a vessel which can be used while the vessel is in operation or is “live”.